The 3 Types of Fasting Schedules

Time-restricted fasting: This method has you fasting for about 12 to 16 hours per day, giving you about eight hours to actually eat. Most people do this by starting at night, skipping breakfast, and eating their first meal around lunchtime. That gives them another seven or so hours to feed themselves until tomorrow.

Modified fasting: This option allows you to eat about 25% of your recommended calorie needs on two fasting days, followed by five days of eating like a human being. It's also called the 5:2 diet.

Alternate fasting: In this less regimented style, you switch between periods of consuming zero-calorie foods and beverages and actual eating. Some fans follow a high-fat or ketogenic diet on their days off from fasting. Others simply stick to a more balanced plan. Regardless, some fasts can end after less than 12 hours, while others can stretch as long as a full week!

What the Research Says

There are a few claims but not much by the way of science in favor of long-term fasting for health or weight loss. Some small animal studies linked the practice with reduced insulin production and sugar uptake in fat cells, leading to a lower risk of chronic disease. The thinking is that fasting may give your vital organs, digestive hormones, and metabolic functions a "break."

With that in mind, a 2017 study published in the Journal of the American Medical Associationfound that there was virtually no difference between people who practice alternate-day fasting and those who simply restrict daily calories.

The other bad news for fasting fans? This trial (arguably the best to date since it examined long-term changes of metabolism and weight loss in humans, not animals) found that LDL or "bad" cholesterol increased in the alternate fasting day group compared to control groups. Other risk indicators stayed the same across groups on this trial and other similar ones.

The Potential Benefits of Fasting

More Purposeful Eating: The biggest advantage stems from the fact many of us eat based on the scenario, not hunger levels. (Raise your hand if you've ever gone to the movies after dinner and suddenly wanted popcorn.) Through IF, you're limiting when you're allowed to eat, meaning you cut back on habit-driven snacking you may not have been aware of. Say you're a person who loves to graze during The Bachelor. If you're "fasting" post 8 p.m., you've automatically cut out munching opportunities — and subsequently, calories.

Better Sleep Habits: If your fasts are time-restricted, the lack of late-night snacking alone could help you go to bed earlier — a crucial component to any weight loss plan. Getting seven hours of sleep per night as been linked to weight management, reduced risk of chronic disease, and improved metabolism.

Smarter Food Choices: Frequently choosing what and when to eat during a given day can leave us susceptible to making snap decisions that ultimately leave us dissatisfied — either immediately or when done consistently over time. But if you know you've only got a certain amount of time to eat, you may make smarter choices when you do. Simplifying and structuring the whole "what should I have for a snack?" scenario is a benefit many fasters appreciate.

Intermittent fasting could help you cut back on late-night snacking and get off to bed sooner, both major upsides when it comes to weight loss.

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The Potential Downsides of Fasting

With all of that said, intermittent fasting plans can also backfire tremendously— especially if your goal is to lose weight. Fasting can lead to nausea, dehydration, and even weight gain over time. No research to date has effectively looked at the long-term effects of fasting on metabolism. You may also eat more than you thought you would during your days of "feasting" too.

Eating real, nutrient-dense foods on a consistent basis fuels us physically, mentally, and emotionally. So if IF works for you, go for it! But if it makes you feel anxious, depressed, or isolated in any way, it may not be the best plan for you personally.

Plus, I'd be remiss to mention who should absolutely not dabble in this eating style: Anyone who's previously struggled with an eating disorder or experienced disordered eating behaviors, or if you're immunocompromised, pregnant, lactating, or on insulin, oral hypoglycemic, or food-metabolizing medications. No matter who you are: Always check with your doctor before starting any new diet plan — especially one that includes fasting!

While research tells us that there may be potential benefits for some people, if severe food restrictions provoke any anxiety, then just don't do it. There's no clear-cut reason to opt out of meals, so stick with consistent eating strategies that work best for you — without any shame or guilt that extreme behaviors can stir up in so many of us.

The Bottom Line

What I like about intermittent fasting is that there may be benefits for some people to prolong (realistically) the time they go without food as it relates to sleep and caloric intake. Population studies have linked eating more at night with an increased risk of obesity, but fasting takes that concept to extreme measures.

If you're considering IF, I'd encourage you to start small and simple: Experiment with an "early bird special" for dinner. Close your kitchen once you're finished, aim to get more sleep overnight, and eat a full breakfast at your usual time tomorrow. Making this one change is an aspect of intermittent fasting we can all get behind.

Jaclyn London, MS, RD, CDN, Good Housekeeping InstituteDirector, Nutrition LabA registered dietitian with a Bachelor of Arts degree from Northwestern University and a Master of Science degree in Clinical Nutrition from New York University, Jaclyn “Jackie” London handles all of Good Housekeeping’s nutrition-related content, testing, and evaluation.

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